One long-term goal of the PI's research program has been to understand nervous system function as influenced by GABA and by clinically significant and abused drugs. The goal of this application for a Fogarty International Research Collaboration Award is to focus on the explicit role of the GABA-A receptor complex in promoting neuronal survival and neurite branching during development. The immediate aim of this proposal is to test the hypothesis that nerve cell survival and complexity of neurite outgrowth are regulated during development by ambient GABA as well as factors which influence the activity of the GABA-A receptor, including barbiturates, benzodiazepines, and neurosteroids. This will be accomplished using primary cell cultures prepared at low nerve cell density from rat cerebellum, cortex and spinal cord. Cell survival will be assayed over 7-10 days in culture using phase contrast optics. For studies of the complexity of neurite development, nerve cells in culture will be stained with tetanus toxin fragment C and visualized using a peroxidase-diaminobenzidine development system. Cell morphometry will be determined utilizing an optical scanning system and "Image" software which will permit the fractile dimension of cells to be calculated. This work is a natural extension of: 1) the PI's research program which is focused on studies of the influence of receptor activation on the expression of GABA-A subunit message and protein during development in primary cell culture; 2) the experience of the foreign collaborator who has studied GABA-A receptor expression in situ and in vitro. While permitting the test of this important developmental hypothesis, the work will increase our understanding of the influence of selected neuroactive drugs during development and will enhance the research capabilities of the foreign coinvestigator by providing collaborative expertise as well as support for supplies and equipment.